The enzymology and regulation of adrenal cortex steroidogenesis will be studied, with particular emphasis on the role of the mitochondrial phospholipid membrane in the control of cytochrome P-450scc-dependent side chain cleavage of cholesterol. The enzymes adrenodoxin reductase, adrenodoxin, and cytochrome P-450 will be purified from beef adrenal mitochondria, and will be studied using stopped flow spectrophotometry, EPR, and UV-visible absorbance spectrophotometry. The ACTH-control mechanism will be studied using cell cultures of an ACTH-responsive mouse adrenocortical cell line. Control by progesterone of 11 beta-hydroxylation has also been observed and will be studied in the purified enzyme system and in the cell cultures.